1. Field of the Invention
The present invention relates to a displacement telemetering system for accurately measuring displacements such as construction error, heat strains and vibrations of an object such as a space antenna reflector.
2. Description of the Prior Art
FIG. 1 shows an example of a space antenna used for communications, broadcasting, observation, etc. The antenna comprises a transmission horn 101 acting as a primary radiator, a sub-reflector 103 for reflecting radio waves transmitted from the transmission horn 101, and a main reflector 105 for reflecting the radio waves reflected by the sub-reflector 103 in a particular direction. The space antenna is a huge structure, and a mirror surface of the main reflector 105 is required to be highly accurate.
To install such an antenna in space, the antenna is folded into a proper size or divided into segments to reduce its size. After launched into the space, the antenna is developed or assembled back to its original shape.
Since the surface of the antenna should be highly accurate, surface accuracy of the reflector 105, etc., should be correctly measured after they are assembled in space, and heat strains caused on the reflector, etc., due to severe temperature changes should also be measured.
FIG. 2 and 3 show conventional displacement telemetering system respectively, for measuring the displacements and vibrations of a remote object.
The system shown in FIG. 2 is provided with a reflecting member 109 arranged on an antenna reflector 107 which is to be measured Light emitted from a light source 11 is intensity-modulated and made incident onto the reflecting member 109 through a scanning mirror 115. The return time of the light made incident onto the reflecting member 109 is measured, and the deformation amount of the reflector 107 is calculated in a displacement operating portion 117. A mirror driving unit 119 changes the inclination angle of the scanning mirror 115 to make light incident onto another reflecting member 109 on the reflector 107 to measure the deformation amount of another measuring point of the reflector 107.
However, in this system the measuring accuracy depends upon an optical range finding system which is based on intensity modulation, so a satisfactory accuracy is not obtainable.
Another conventional telemetering system shown in FIG. comprises an object 120 to be measured, an LED 121 as a light source, and a lens system 123 which receives light emitted from the LED 121 to provide a light beam. The beam is divided by a dividing mirror 125 into two component beams which are orthogonal to the optical axis of the incident beam. The divided component beams are focused onto optical sensors 129a and 129b through lenses 127a and 27b, respectively. Then, the deformation amount of the object 120 is measured by a light spot position sensor
In this system, the LED 121 as a light source is disposed on the object 120 to be measured, so wiring will need to be provided for the object 120. Further, if the energy source for the LED 121 is consumed, it will be difficult to measure the displacement of the object 120 because the energy source of the LED is difficult to recharge due to the remoteness of the object 120. In addition, if the number of measuring points of the object 120 is increased, the substantially same number of optical systems, each comprising the lens system 123, dividing mirror 125, lenses 127a and 127b and optical sensors 129a and 129b, should be provided, so the system becomes complicated and the number of parts is increased.
Referring to FIG. 4, there is shown a prior art system for detecting a configuration of an arrangement of a solar array 131. In this system, a star sensor 135 is constructed to detect a reflected light from corner cube reflectors 133 attached to the solar array 131 to measure the positions of the reflectors 133. However, since the star sensor 135 is designed to have a wide geometric field to detect a direction of the system facing to the star, it is impossible to measure displacements of the reflectors 133.
As described in the above, it is difficult to accurately measure the displacement of an object with the conventional telemetering systems which are based on intensity modulation.
In addition, to disposed a light source on an object to be measured, wiring would need to be arranged on the object. Once the energy source of a light source disposed on the object is consumed, it becomes impossible to measure the displacement of the object which is remotely located. If the positional displacement of the light source is measured by the light spot position sensor to determine the displacement of the object, the measurement accuracy is still not satisfactory under the wide geometric field, and optical systems would need to be prepared in the substantially same number as that of measuring points of the object, so the system will become complicated as the number of parts is increased.